In this method, you press a key combination to insert a char. This is
great solution if you just need a few chars that's frequently used. If
you need more than say 50 chars, you need to add more modifier key combinations,
it quickly become a problem of remembering which chars are what key. So,
this method isn't good if you need to input a lot math for example, because
there are few hundreds of math symbols, and different people have different
set of chars that's frequently used for them.

The disadvantage is that it's slower. If you need let's say only 10 to 30 chars that you need to type every few minutes, for example, say the acute e é in some language, then the 2-keys by
【AltGraph+e】 is faster.

However, the 2 methods can both be used. That is, have a AltGraph layout, but also have the abbrev system.

When is Hotkey Pressed

The hotkey can be pressed before you type the abbrev, or, it can be pressed after. Or, it can be completely eliminated by a automatic change.

For example, in emacs, you press
【Ctrl+x8】, then type
'e
then you get é. This is a example of hotkey first. [see Emacs and Unicode Tips]

Changes to my Emacs Elisp Code

So, yesterday, i started to organize my several elisp code related to inputting special math symbols to a unified minor mode. For example, i had the following code that sets up a
emacs hyper key to insert chars: